I've been adding the newest chicks into the same brooder with the NY chicks. So there are two little bitty things in with larger chicks. It has gone very, very well. The only problem has been the larger chicks bowling over the babies when they get up and run, whilst the little babies are still napping or just in their way. But they pop right back up and are perfectly fine. No pecking, no harassing, no troubles.
I have a third little chick which was badly shrink-wrapped and it's now resting, still covered in some shell and membrane, but all moistened and in very high humidity in the 'bator. It can breathe and stretch and I want to see if it will break free now that the membrane is wet again and some of the most constricting parts have been removed.